Medical and dental instruments used in both routine examinations and more complicated surgeries require sterilization before use. In the past, these instruments have been sterilized either as individual instruments loosely placed in the autoclave or organized in plastic or metal storage cassettes. However, both these methods have led to certain problems.
When loose instruments are individually placed in the autoclave and not secured, they may strike against each other or against the interior of the autoclave, causing harmful metal-to-metal contact. Since the instruments are delicate in nature, the resulting contact can cause damage and render them useless or subject to contamination. Additionally, because the instruments are not secured in any set order, they must be reorganized before the next surgical procedure. This process is time-consuming, and when instruments from different types of surgeries are autoclaved together, even more time is spent on sorting and reorganizing the specific instruments for each type of surgery.
On the other hand, when instruments are sterilized and organized in conventional cassettes, a different set of problems arises. At lower production volumes, metal cassettes are cheaper than plastic cassettes but when these metal cassettes are normally constructed from reinforced wire mesh they are subject to rust, discoloration, breakage, and debris entrapment. Secondly, wire cassettes are not stackable, and therefore take up too much space during autoclaving and storage. Thirdly, when the instruments are placed into these cassettes, metal-to-metal contact again occurs between the instruments and the cassette. This contact causes the same problems as when the instruments are sterilized loosely, inasmuch as the instruments become damaged or scratched and thus subject to contamination.
Still another problem arises with conventional metal trays used for sterilization and storage of medical and dental instruments. Currently, the instruments are held in place only by closing the cassette cover. If the cover loosens or is not properly secured, it may release during the loading and unloading of the trays from the autoclave or from storage. Because the instruments are not otherwise secured within the cassette, they may fall out and be damaged. Furthermore, if instruments are loose within a cassette, the same damaging metal-to-metal contact between instruments, or between instruments and the cassette, may occur.
Finally, there is a problem with the amount of storage available for medical and dental instruments in the cassettes now available. In U.S. Pat. No. 4,854,475, for example, space for placing and securing instruments is only provided in the bottom portion of the cassette, while the covers are left unutilized. As a result, fewer instruments may be sterilized at one time, which leads to more time spent autoclaving. This lack of space management not only affects autoclaving time, but also limits storage space for the instruments after they emerge from the autoclave.
U.S. Pat. No. 4,959,199 partly addresses this problem, in that it provides an instrument sterilization cassette which separates into individual trays, each capable of storing instruments and each having a cover member which helps to retain the instruments in place therein. But the cover member is completely detachable from the tray, and when separated may become lost. In addition, the cassette of this patent is entirely molded from plastic resin materials, a method of manufacture which is relatively expensive at low production volumes.
Because of these considerations, there exists a need to provide a two-tier cassette to hold medical and dental instruments during and after sterilization, which overcomes the above-mentioned disadvantages, and which can, if desired, be manufactured largely from sheet metal stampings.